Thermal protector

ABSTRACT

A thermally actuable switch is provided with two conductive members having a first portion of each selectively contacting and a second portion of each separated by an insulating material, at least one of the conductors being spring biased to one position and being held in a second position by a temperature sensitive material which collapses when a predetermined temperature has been reached.

Unite States Patent [191 Web] [ July 30, 1974 THERMAL PROTECTOR [75] Inventor: Glenn E. Wehl, North Canton, Ohio [73] Assignee: Portage Electric Products Inc.,

North Canton, Ohio [22] Filed: Sept. 24, 1973 [21] Appl. No.: 399,819

[52] US. Cl. 337/407, 337/414 [51] Int. Cl. H01h 37/76 [58] Field of Search 337/407, 401, 402, 403, 337/404, 405, 406, 408, 411, 413, 148, 157,

[56] References Cited UNITED STATES PATENTS 295,760 3/1884 Hill 337/407 FOREIGN PATENTS OR APPLlCATlONS 594,183 9/1925 France 337/414 89,756 9/1920 Switzerland 337/414 Primary Examiner-Harold Broome Attorney, Agent, or Firm-Ryder, McAulay, Fields, Fisher & Goldstein [57] ABSTRACT A thermally actuable switch is provided with two conductive members having a first portion of each selectively contacting and a second portion of each separated by an insulating material, at least one of the conductors being spring biased to one position and being held in a second position by a temperature sensitive material which collapses when a predetermined temperature has been reached.

7 Claims, 5 Drawing Figures 1 THERMAL PROTECTOR BACKGROUND OF THE INVENTION One-shot thermal switches which actuate upon the switch reaching a given upper temperature are well known in the art. Because of recently instituted safety requirements, the use of such switches has increased to a great extent.

The switches manufactured to date are generally complex and have a number of moving parts. For example, such switches are shown in US. Pat. Nos. 2,934,622 Massar and 3,517,366- Patrichi. These patents describe switches which are actuable upon a particular temperature being reached and describe a spring loaded plunger which is released upon decomposition of a thermodegradable material to actuate the switch.

In US. Pat. Nos. 3,l80,958 and 3,519,972-Merrill, similar switches are shown where a plunger is actuated to sever a wire. The severing of the wire is an actuatio of the switch.

In both of the described systems, though actuation of the device is occasioned by decomposition of a thermally degradable material in the device reaching a particular temperature, a number of moving parts are'required to provide 'a functioning switch.

The number of moving parts required for the devices of the prior art is excessive and a switch actuable under the same conditions, but with a minimum of moving parts would be most desirable.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention, athermally actuable switch, where the switch is actuated from one position to another upon the device being subjected to a high enough temperature, is provided with a minimum of moving parts. As such, the device can be manufactured for a far lower cost than is possible with the devices of the prior art and, further, is more foolproof.

In accordance with the present invention two contacts are provided within a thermally actuable switch. The first contact is formed of spring metal and is held in a first position by a thermally decomposable material. The second contact is provided by, or adjacent to, a case in which the spring metal member is mounted. Upon reaching a given temperature, the spring metal member is free to move from a position where it contacts the case to a position away from the case, so that a contact is broken, or is free to move from a position where it does not contact the case'to a position where it does contact the case, so that a contact is made. The case, itself, can be rendered conductive, as by silver flashing, or a separate contact member may be attached to one or more walls of the case and the spring metal member adapted to contact this additional member. Obviously the spring metal member, while contacting the case or a contact attached to the case at one end, is insulated from the case at the opposite end.

Thus, only one movable member is provided in the thermally actuable switch of the present invention. This movable member acts as a contact and further acts to make or break a contact within a case. As such, the construction of the switch is simpler, more economic, and more foolproof than those of the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a perspective view of a switch according to the present invention including contacts to the case and to the spring metal member;

FIG. 2 is a sectional view along the line 2--2 of FIG.

'1 showing the spring metal member in contact with the case;

FIG. 3 is a view similar to FIG. 2 where the spring metal member is out of contact with the case;

FIG. 4 is a sectional view along the line 4-4 of FIG. 3 showing the spring metal member mounted within insulating members; and

FIG. 5 is an assembly view showing the parts of the thermally actuable switch of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, a thermally actuable switch 1 is illustrated having a case 1 and a spring metal arm 3. The spring metal arm is insulated from the case, at its entry end, by insulator members 4 and 5. In order to firmly seal the spring metal member 3 within the insulating members 4 and 5, and particularly within case 2, an epoxy or other resinous insulator 6 may be placed within the structure to firmly hold the conductor 3 in place.

Conductors l0 and 11 are attached to case 2 and spring metal member 3, respectively to provide connection to the electrical circuit in which the thermal switch is to operate. These conductors are shown as soldered to the case and spring metal member at 12 and 13, but any means by which the conductors l0 and 11 are securely fastened, mechanically and electrically, to the thermal switch device can be employed.

In the construction illustrated, particularly in FIG. 2, the spring metal member 3 is biased to a position intermediate the top and bottom of the case 2, as particularly indicated in FIG. 3. However, a body of thermally decomposable material 20 acts to urge the spring metal member 3 into a position adjacent the wall of the case 2. When the thermal switch 1 is connected in an electrical circuit, with the members in the position shown in FIG. 2, current will flow from conductor 11 through spring metal member 3 to case 2 and then through conductor 10 to the circuit. In this form, a circuit is thus completed.

In order to assure that the case is properly conducting, a silver flashing 21 is applied to at least that surface 7 of the case 2 which is to be contacted by the spring metal member 3. In place of the silver flashing, a beryllium-copper strip may be placed in the same position to assure adequate contact. While the flashing 21 is illustrated as occupying only that portion of the casing which is to be contacted by contact 3, it will of course be appreciated that in normal practice, the entire inner surface of the case will be silver flashed. Similarly, though it is indicated that a beryllium-copper strip may be attached to the case in the position shown at 21, more of the case can be so treated, so long as that portion to be contacted by spring metal member 3 is so covered.

The member 20 is formed of any of the materials, now well known in the art, which melt, disintegrate, or otherwise lose rigidity almost instantaneously upon reaching a given temperature. Below that temperature,

the member 20 is rigid and is adequate to resist the pressure of spring metal member 3, so as to hold the spring member in the desired position. The specific formulation of this material is not critical to the present invention, but only the function of the material.

Referring .to the accompanying drawings, in operation the switch as illustrated provides a circuit, as previously indicated. When the ambient temperature surrounding the switch 1 reaches a temperature, as determined by the composition of member 20, member 20 disintegrates to a degree that it is no longer capable of urging spring metal member 3 against case 2. The right end, as viewed in the drawings, of spring metal member 3 is then free to assume its normal position, as indicated in FIG. 3, so that contact is broken and current no longer flows between conductors l and 11.

While the thermal switch 1 has been illustrated as one wherein contact is broken when a given temperature is reached, it may equally well be formed in such a fashion that a contact is made when a given temperature is reached. To accomplish that, spring metal member 3 would have a normal position such that its right end would contact the lower portion of case 2 as illustrated in FIGS. 2 and 3. A member 20 would then be inserted to urge spring metal member 3 to a position intermediate the upper and lower walls of case 2, or to the position illustrated in FIG. 3. Under these circumstances, when member 20 collapses through disintegration, spring metal member'3 is free to move downwardly to its normal position so as to contact the bottom portion of the case and establish a contact.

In accordance with the present invention a simply operated, economically constructed thermal switch has been illustrated. As indicated, the switch can operate to establish a contact upon the ambient temperature surrounding the switch reaching a predetermined value, or can be used to break a contact under the same circumstances. The invention should not be considered as limited to the specific embodiments illustrated and described, but only as limited by the appended claims.

I claim:

1. A thermally actuable electric switch comprising:

a. a conductive outer casing having a first end and a second end;

b. a spring metal member within said casing having a first end and a second end;

c. insulating members electrically insulating said first end of said casing from said first end of said spring metal member such that said spring metal member occupies a second position within said case; and

d. a thermally decomposable member within said casing, said thermally decomposable member being in .direct contact with said spring metal member and urging said second end of said spring metal member to a first position relative to the second end of said casing.

2. The thermal switch of claim 1 wherein said second position of said spring metal member is out of contact with said casing and said spring metal member is urged into contact with said casing as a first position by said thermally decomposable member.

3. The thermal switch of claim 1 wherein the second position of said spring metal member is in contact with said casing and said spring metal member is urged to a first position out of contact with said casing by said thermally decomposable member.

4. The thermal switch of claim 1 wherein the inner wall of said case is provided with an electrically conductive material at least at the point of contact of said spring metal member.

5. The thermal switch of claim 4 wherein said elecrically conductive material is a silver flashing.

6. The thermal switch of claim 4 wherein said electrically conductive material is a beryllium-copper strip.

7. The thermal switch of claim 1 wherein the first end of said spring metal member and said casing are mechanically and electrically connected in an electrical circuit. 

1. A thermally actuable electric switch comprising: a. a conductive outer casing having a first end and a second end; b. a spring metal member within said casing having a first end and a second end; c. insulating members electrically insulating said first end of said casing from said first end of said spring metal member such that said spring metal member occupies a second position within said case; and d. a thermally decomposable member within said casing, said thermally decomposable member being in direct contact with said spring metal member and urging said second end of said spring metal member to a first position relative to the second end of said casing.
 2. The thermal switch of claim 1 wherein said second position of said spring metal member is out of contact with said casing and said spring metal member is urged into contact with said casing as a first position by said thermally decomposable member.
 3. The thermal switch of claim 1 wherein the second position of said spring metal member is in contact with said casing and said spring metal member is urged to a first position out of contact with said casing by said thermally decomposable member.
 4. The thermal switch of claim 1 wherein the inner wall of said case is provided with an electrically conductive material at least at the point of contact of said spring metal member.
 5. The thermal switch of claim 4 wherein said elecrically conductive material is a silver flashing.
 6. The thermal switch of claim 4 wherein said electrically conductive material is a beryllium-copper strip.
 7. The thermal switch of claim 1 wherein the first end of said spring metal member and said casing are mechanically and electrically connected in an electrical circuit. 